In the manufacture of paper, a slurry is ejected from a headbox to the forming wire or wires of the machines. The outlet from the headbox must be accurately formed to control the jet thickness transversely of the machine and thereby form a paper web of uniform cross-machine basis weight profile, i.e., having substantially the same basis weight across the width machine. To attain this result the slice lip which defines an edge of the orifice, i.e., extending transversely across the paper machine, must be accurately positionable and requires discrete adjustments at spaced locations transversely of the web to adjust locally the basis weight of the paper being formed. The slice edge, i.e., the operative or effective edge of the slice lip, therefore is not normally parallel with the apron lip that forms the opposite side of the headbox outlet, since as above indicated minor variations in flow across the headbox are adjusted by adjusting locally the relative spacing between the slice lip edge and the cooperating apron lip. Thus the slice lip itself must have at least limited flexibility so that it may be deformed locally to make these adjustments.
The slice lip, since it forms one of the working edges of the orifice outlet from the headbox, is obviously subjected to wear and on occasion may be damaged by foreign material or the like passing through the headbox and scraping the slice lip. When this happens or when the slice lip wears significantly, it is necessary to remove the slice lip and replace it with a new one or with another slice lip that has been reconditioned. This practice has been carried on in the paper making industry it is believed since the inception of the adjustable and replaceable slice lip was introduced.